Device for purging pitot tubes



April 30, 1968 Filed June l1, 1965 V. W. HANSON DEVICE FOR PURGING PITOT TUBES 2 Sheets-Sheet l April 30, 1968 v. w. HANsoN 3,380,298

DEV [CE FOR PURGNG PITOT TUBES Filed June 11, 1965 2 Sheets-Sheet :'-1

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(4,53 maf/IW United States Patent O 3,380,298 DEVICE FOR PURGING PITOT TUBES Victor Wendell Hanson, Garden City, Mich., assigner to Ajem Laboratories, Inc., Livonia, Mich. Filed June 11, 1965, Ser. No. 463,079 3 Claims. (Cl. 73-182) This invention relates to a device and method for clearing Pitot tubes.

It has been found in measuring air velocities under severe test operating conditions that t-he Pitot tubes may become clogged in as short a time as -15 seconds after which serious inaccuracies and irregularities appear in the observed values for velocities.

An air valve -manifold system was designed to operate first to cut off the airflow line to the manometer; secondly, to open a valve from a high pressure line to purge the Pitot tube; thirdly, to close the high pressure valve and open the line from Pitot tube to the atmosphere to quickly equalize pressure; fourthly, to close the equalizing valve; and fthly, to open the valve in line from Pitot tube to manometer so a pressure reading could be recorded before the Pitot tube would start plugging again. Before each pressure reading the above cycle was repeated to purge the Pitot tube and equalize the air line.

In the drawings:

FIGURE l is a diagrammatic representation of the hydraulic part of the apparatus; and

FIGURE 2 is a -circuit diagram of the electrical controls for the valves shown in FIGURE 1;

FIGURES 3, 4 and 5 are diagrammatic representations of the fluid ow and connections of apparatus such as is shown in FIGURES 1 and 2, during, respectively, a purge, a vent and a reading cycle.

FIGURES 1 and 2 show pneumatic and electrical schematic diagrams of my new electrically operated system in which the three valves 10, 12 and 14 are activated by solenoids 16, 18, and 20. By turning a three position switch 22 the appropriate valve combination is selected.

When Pitot tube measurements are to be made under severe conditions, the apparatus is subjected to a purge cycle to keep the internal areas clean. Switch 22 which controls operation of solenoids 16, 18 and 20 is put in position A (FIGURE 2) which opens valve 10 to admit high pressure from 36 and 26 to valves 12 and 14, and valves 12 and 14 are open from lines 23 and 21 to ports 34 and 34 and thence to Pitot tube 27 through lines 23' and 21 (diagrammatically shown at the bottom of FIGURE 1). Note that the lines 23 and 21 are closed from the ports 44 and 44 so that the high pressure fluid does not go to the manometer 29 (see FIGURE 3). After thus purging Pitot tube 27 and its connecting lines by blowing them out with high pressure Huid., switch 22 is turned to position B, which deactivates solenoid 16 so as to turn valve 10 to the position shown in FIGURE 4 and thereby vent lines 21 and 23 through 31 to the atmosphere. Note, with switch 22 -at position B, valves 12 and 14 remain closed to manometer, and valve 10 remains turned (see FIGURE 4) so that it opens the lines 21 and 23 from the Pitot tube through valves 12 and 14 to the atmosphere to equalize pressure in these lines. For manometer readings the switch 22 is at position C, valve 10 remains vented to atmosphere and becomes closed to valves 12 and 14, when the solenoids 18 and 20 turn their respective valves 12 and 14 to complete the pneumatic circuit of Pitot tube 27 to manometer 29. After reading the manometer, the switch is moved to position A to resume purging.

With this arrangement even a new observer can operate the device with good assurance of accurate results and with no diticulty in following proper procedure.

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Another distinct improvement was the encasement of the air manifold valves, switches and accessory components in a metal box 25. When temperatures are below freezing at site of sampling, the box can be equipped with thermostatic electric heater to maintain a selected temperature and prevent freezing. Accurate measurements of air velocities are made even in collector installations where there was high air transport of liquid droplets and solids.

Another feature advantageously combined in my invention is the compressed air line filter 24 'and condensed liquid trap located in the gas pressure system prior to the solenoid valve system just described, which insures clean dry gas with which to purge the Pitot tubes.

The purposes served by this manifold are to:

(l) Maintain clean passages in both static and total pressure (velocity) ports of Pitot tubes.

(2) Allow trouble free transition from purge to read in the operating cycle.

(3) Permit use olf hemispherical tip or tapered tip Pitot tubes of unity static pressure correction factor.

(4) Permit minimum time lapse for steadying out manometer uid at level point or point of last reading and, therefore, permit rapid reading.

This `device works on normal in-plant compressed air at line pressures of 20-100 p.s.i. A compressed air filter 24 removes solids and liquids and thereby protects the solenoid valves.

The needle Valve adjustment 26 permits control of air ow rate to Pitot tube lines but operates below a pressure which would blow the connection tubes off from the connections.

Proper operation may be supervised -by a visual press-ure gauge 28.

The solenoid valves lll-16 12-18, 14-26, are spool type, normally closed, three way valves. 10-16 is for primary ow control, directing the compressed air to either or both of the other two valves for purging the Pitot tubes, or venting the system to atmosphere. The other two solenoid valves control the purge and read cycle between Pitot tube and manometer.

A single pole, three position switch 22 actuates the three cycles respectively.

Indicator light 30 in the purge circuit shows when the solenoid valve 16-111 is activated. The circuit is connected to a v. source by a plug 32 with a ground connection.

As the manometer, Pitot tube, and connections are well known in the art, they have been indicated diagrammatically on the bottom of FIGURE l.

A heater may be included to protect the valves against freezing and sticking, and to this end all components, as well as the heater are enclosed in a suitable box 25.

Sequence of operation (A) Purge cycle:

(1) Valve 10 is opened to feed air to -both valves 12 and 14 and is closed against the atmosphere vent 31.

(2) Valves 12 and 14 are closed to the manometer circuit and open from the pressure gas supply valve 10 to the Pitot tube.

(B) Vent cycle:

(1) Valve 10 (after being open from the gas pressure supply control Valve 26 to solenoid valves 12 and 14 and, through them, to the Pitot tube for purging) is operated by its solenoid 16 to return it to its normally closed position so as, to cut o valves 12 and 14 from the pressure supply line 36 and to exhaust lines 21 and 23 to the atmosphere through vent 31.

(2) Valves 12 and 14 remain closed to the manometer and open to the Pitot tube 27 through the lines 23, 23',

0 21, 21', 34 and 34', so that it and its connections are depressurized.

(C) Read cycle:

(1) Valve 10 is now operated to close oi the valves 12 and 14 from the gas pressure supply and quickly open them to the atmosphere to prevent any possible leakage of the purging gas pressure into the manometer connections.

(2) Valves 12 and 14 are opened to connect the Pitot tube and manometer but to close off the connection to atmosphere through valve l0.

(3) With the valves in this situation the standard Pitot tube circuit is complete, and the manometer reading is taken and can be relied upon as accurate.

(D) The sequence is repeated as required for each reading, with the purge cycle remaining on during all movement and positioning of the Pitot tube.

Advantages of manifold (A) Enables the use of any Pitot tube under severe plugging conditions of either liquid or solid particles or both.

(B) In contrast to ordinary manual sequencing the single switch electrically operated manifold has eliminated operator confusion and is time saving.

(C) By using this Pitot purge manifold the standard, no-static-pressure-correction Pitot tubes may be used.

(D) Being of leak tight valve construction no time loss is incurred with the manometer fluid starting and gradually returning to zero after each reading, thus insuring the shortest time interval to determine the velocity pressure reading for each point. With the manometer iluid near the actual reading range any immediate plugging of the Pitot tube is immediately indicated by the rapid shift in manometer uid and the system is repurged and the reading retaken.

What I claim is:

1. A device for maintaining accuracy of readings of a Pitot tube with manometer which comprises three-Way valve means adapted to connect the static side of the Pitot tube, alternatively, with the static side of the manometer or a supply of gas under pressure; a second threeway valve means adapted to connect the velocity pressure side of the Pitot tube with the velocity pressure side of the manometer or with a supply of gas under pressure; a third valve means adapted, alternatively, to connect both of said valves to, and cut off both of said valves i from, a supply of said gas under pressure and, alternatively, to open them to the atmosphere to exhaust said gas therefrom, and ymeans for operating all of said valves in appropriate sequence.

2. A method of measuring velocity 0f ow of a uid in a stream by exposing a Pitot tube in said stream and connecting the Pitot tube to a sensitive pressure comparison instrument, and measuring the increase of pressure in said Pitot tube, which is characterized by shutting oit said Pitot tube from the sensitive instrument, passing a purging uid to and through an orifice of said Pitot tube, in an outward direction and under pressure substantially higher than the external pressure to which said orifice is exposed, shutting od said purging fluid from said orifice and venting said pressure of the purging uid, and then, with said orifice exposed in said stream, reconnecting the Pitot tube to said instrument and measuring the pressure increase in the Pitot tube due to inertia of said stream.

3. A method as defined in claim 2 in which the velocity pressure is determined by an orifice facing upstream in said flow and a static pressure, for comparison with the velocity pressure, is determined by an oriiice facing in a direction normal to the fluid iiow in said stream, and the purging uid under pressure is passed outward through said orices to keep them clear for comparing the velocity pressure of said ilow against said rst-named orifice with the static pressure on the second-named orifice, shutting off said purging fluid from said orice and venting said purging fluid pressure, and promptly allowing Huid from said stream to pass through said orifice and comparing the pressures at this orice with that of the orifice facing upstream.

References Cited UNITED STATES PATENTS 1,810,907 6/1931 Cole 73-212 2,016,926 10/1935 Iosepowite 15-3.5l 2,662,402 12/1953 Inca et al. 73-212 3,044,908 7/ 1962 Baldi 134-37 FOREIGN PATENTS 355,921 9/ 1931 Great Britain.

LOUIS R. PRINCE, Primary Examiner.

N. B. SIEGEL, Assistant Examiner. 

1. A DEVICE FOR MAINTAINING ACCURACY OF READINGS OF A PITOT TUBE WITH MANOMETER WHICH COMPRISES THREE-WAY VALVE MEANS ADAPTED TO CONNECT THE STATIC SIDE OF THE PITOT TUBE, ALTERNATIVELY, WITH THE STATIC SIDE OF THE MANOMETER OR A SUPPLY OF GAS UNDER PRESSURE; A SECOND THREEWAY VALVE MEANS ADAPTED TO CONNECT THE VELOCITY PRESSURE SIDE OF THE PITOT TUBE WITH THE VELOCITY PRESSURE SIDE OF THE MANOMETER OR WITH A SUPPLY OF GAS UNDER PRESSURE; A THIRD VALVE MEANS ADAPTED, ALTERNATIVELY, TO CONNECT BOTH OF SAID VALVES TO, AND CUT OFF BOTH OF SAID VALVES FROM, A SUPPLY OF SAID GAS UNDER PRESSURE AND, ALTERNATIVELY, TO OPEN THEM TO THE ATMOSPHERE TO EXHAUST SAID GAS THEREFROM, AND MEANS FOR OPERATING ALL OF SAID VALVES IN APPROPRIATE SEQUENCE. 